Plant for the Plasma Surface Treatment of an Alveolar Sheet of Plastic Material

ABSTRACT

The plant is intended for performing the plasma surface treatment of an alveolar sheet ( 10 ) of plastic material having a first and second outer face surface ( 12, 14 ) and an inner alveolar surface ( 16 ). The plant comprises means able to allow the simultaneous and independent treatment of each of said outer surfaces ( 12, 14 ) and inner surface ( 16 ) with a respective plasma ( 96, 98, 100 ) with which a process fluid is associated, said fluid being deposited on one of said surfaces ( 12, 14, 16 ).

The present invention relates to a plant for the plasma surfacetreatment of an alveolar sheet of plastic material.

One object of the present invention is to provide a plant of the typeindicated above, which is operationally simple and reliable and able toensure a high degree of versatility in terms of performance.

This object is achieved by means of a plant having the featuresspecifically described in claim 1 below. The claims dependent on claim 1indicate preferential features of the plant according to the invention.

By means of the plant according to the present invention it is possibleto perform any combination of treatment of the two outer face surfacesand inner alveolar surface of the sheet. In particular, it is possibleto treat all three of these surfaces in a different or similar way orachieve any intermediate condition. Moreover, it is possible to performthe treatment of only one or two of these surfaces and not treat theremaining surface(s).

A further subject of the present invention consists of the use of aplant of the type indicated above for the plasma surface treatment of analveolar sheet of plastic material.

Further advantages and characteristic features of the present inventionwill emerge from the detailed description which follows, provided by wayof a non-limiting example with reference to the accompanying drawings inwhich:

FIG. 1 is a schematic illustration of a plant for the plasma surfacetreatment of an alveolar sheet of plastic material;

FIGS. 2 a to 2 d illustrate schematically respective types of surfacetreatment which can be carried out on the various surfaces of the sheetof plastic material;

FIG. 3 shows schematically the structure of an element of an electrodeof the plant according to FIG. 1;

FIGS. 4 a to 4 c show schematically respective types of surface coatingof the sheet of plastic material; and

FIGS. 5 a to 5 b show schematically a variation of embodiment of theplant according to the invention.

FIG. 1 shows schematically a plant for the plasma surface treatment ofan alveolar sheet 10 of plastic material having (cf. FIG. 2 a) a firstouter face surface 12 and a second outer face surface 14 and an inneralveolar surface 16. The sheet 10 may be, for example, a flat sheet ofpolycarbonate with a thickness of between 10 and 50 mm. FIG. 1 shows,moreover, an extruder 18 which is conventional per se and from which thesheet 10 to undergo plasma treatment is continuously extruded. The plantcomprises a first pair of electrodes formed by a first electrode 20 anda second electrode 22 arranged facing each other so as to define aninterstice inside which the sheet 10 is displaced and extruded in adirection parallel to that of longitudinal extension of its alveoli. Thefirst and the second electrodes 20, 22 thus face respectively the firstand the second outer surface 12, 14 of the sheet 10. The aperture of theinterstice may be adjusted by varying the distance at which the firstand the second electrodes 20, 22 are arranged.

A second pair of electrodes 20 a, 22 a having characteristics basicallysimilar to those of the first pair is arranged downstream of the firstpair of electrodes 20, 22 (with reference to the displacement of thesheet 10).

The various electrodes are provided with respective means for supplyinga carrier gas, able to be converted into plasma, and a process fluid.

The supplying means of the first electrodes 20, 20 a include a storagetank 24 for a first carrier gas, from which there extends a deliveryline 26 having three branches 28, 30, 32. The branch 28 is joined by aline 34 from a storage tank 36 for a first process fluid. Downstream ofthis junction the branch 28 has a vaporizer 38 and then leads into thefirst electrode 20. A line from a storage tank 42 for a first processfluid is joined to the branch 30. Downstream of this junction the branch30 has a vaporizer 44 and then leads to the first electrode 20 a. Thebranch 32 is joined by a line from the storage tank 42 for a firstprocess fluid. The branch 32 terminates in an atomizer device 46arranged between the two first electrodes.

The means for supplying the second electrodes 22, 22 a include a storagetank 48 for a second carrier gas, from which a delivery line 50 withthree branches 52, 54, 56 extends. The branch 52 is joined by a line 58from a storage tank 60 for a second process fluid. Downstream of thisjunction the branch 52 has a vaporizer 62 and then leads into the secondelectrode 22. The branch 54 is joined by a line 64 from a storage tank66 for a second process fluid. Downstream of this junction the branch 54has a vaporizer 68 and then leads into the second electrode 22 a. Thebranch 56 is joined by a line 69 from the storage tank 66 for a secondprocess fluid. The branch 56 terminates in an atomizer device 70arranged between the two second electrodes 22, 22 a.

Each first electrode 20, 20 a has a modular structure and is formed by aplurality of modular elements 72 arranged in succession. In turn, eachelement 72 (FIG. 3) comprises a metal body 74 acting as an anode andhaving, in the portion directed towards the interstice, a cavity 76which is open outwards and inside which a conductive material acting asa cathode 78 is arranged. A layer of dielectric material 80 lines thewalls of the cavity 76 and isolates the anode 74 from the cathode 78,while the surface 82 of the metal body directed towards the sheet 10 islined with ceramic material, having a high secondary emissioncoefficient.

The metal body 74 moreover has, formed therein, passages for conveyingcarrier gas and process fluid, which are directed towards the first facesurface 12 of the sheet 10. FIG. 3 shows the inlet opening of thepassages which is indicated by the reference number 84.

The metal body 74 is also provided with passages 86 for conveying adiathermic fluid so as to allow the temperature of the element 72 to becontrolled in the desired manner.

The second electrodes 22, 22 a too have a modular structure and each ofthem is formed by a plurality of elements substantially similar to thoseof the first electrodes 20, 20 a.

The plant also comprises (FIG. 1) means for supplying into the alveoliof the sheet 10 a third carrier gas, able to be converted into plasma,and a third process fluid. These latter supplying means include astorage tank 88 for the third carrier gas, from which there extends adelivery line 90 joined by a line 92 from a storage tank 94 for thethird process fluid. The line 92 then enters into the extruder 18 andemerges opposite the alveoli of the sheet 10 which is being extruded.

During operation of the plant described above, which typically occurscontinuously and at atmospheric pressure, the sheet 10 leaving theextruder 18 passes through the interstice defined by the first pair ofelectrodes 20, 22 at a speed usually of between 1 and 10 m/min andundergoes treatment with the desired process fluids on the various outerface surfaces 12, 14 and inner alveolar surface 16.

By activating only the means supplying the first carrier gas and thefirst process fluid as well as the passage of electric current betweenanode 74 and cathode 78 of the elements 72 of the first electrode 20,the formation of plasma 96 is caused between the first electrode 20 andthe first outer face surface 12, resulting in the deposition, on thelatter, of a layer of the first process fluid (FIG. 2 a).

By activating also the means for supplying the second carrier gas andthe second process fluid and adjusting the distance of the secondelectrode 22 from the second outer face surface 14 to a value of between1 and 5 mm and preferably between 1 and 3 mm, the formation of plasma 98between the second electrode 22 and the second outer face surface 14 iscaused, resulting in the deposition, also onto the latter, of a layer ofthe second process fluid (FIG. 2 b).

Activating instead the means supplying the third carrier gas and thethird process fluid causes the formation of plasma 100 inside thealveoli, resulting in the deposition, on their surface 16, of a layer ofthe third process fluid (FIG. 2 c).

Activating simultaneously all the various means supplying the carriergases and the process fluids causes the deposition, on the various outerface surfaces 12, 14 and inner alveolar surface 16, of the respectiveprocess fluids (FIG. 2 d).

The various carrier gases used may be identical or different from eachother and chosen from among those conventionally used for producingplasma, such as helium for example. The various process fluids used maybe identical or different from each other and chosen from among thoseconventionally used for imparting to the corresponding surface desiredproperties such as anti-drop, anti-condensation, water-repellent,anti-scratch, anti-UV, IR reflection, conductivity, anti-electrostaticand similar properties. Specific examples of process fluids aretetraethyl orthosilicate, hexamethyl disiloxane, octamethylcyclotetrasiloxane, di(ethyleneglycol)ethyl ether acrylate, allylicalcohol, allyl amine, acrylic acid, diethylene glycol, glycidylmethacrylate, 3-glycidoxypropyldimethoxysilane, 3-(trimethoxysylil)propyl methacrylate.

The modular structure of the electrodes 20, 22 allows the configurationof the latter to be varied so as to adapt it to the type and to thequantity of process fluid to be applied. Moreover, owing to the presenceof the passages 86 for conveying a diathermic fluid inside each element72, the temperature of the latter may be adjusted independently of eachother, so as to allow the formation of the desired temperature profile.The maximum power density which can be withstood by the electrodes 20,22 is in the region of 100 W/cm².

The sheet 10 provided with a first coating layer 102 (indicatedschematically in FIG. 4 a with reference to the case where only thefirst face surface 12 is coated) then passes through the intersticedefined by the second pair of electrodes 20 a, 22 a and undergoes afurther treatment in a manner basically similar to that described withreference to the first pair of electrodes 20, 22. FIG. 4 b shows (againwith reference to the case where only the first face surface 12 iscoated) the sheet 10 emerging from the interstice defined by the secondpair of electrodes 20 a, 22 a, with a second coating layer 104 on top ofthe first layer 102.

In this case, the atomizer device 46 allows delivery, onto the sheet 10,of the first process fluid before plasma treatment which is performed onthe already coated sheet 10. By interrupting delivery of the atomizerdevice 46 it is instead possible to deliver the first process fluidtogether with the carrier gas into the electrode 20 a or it is alsopossible to adopt a mixed delivery procedure. Using the same firstprocess fluid for supplying the two first electrodes 20, 20 a, the twocoating layers 102, 104 will have the same chemical nature, albeit withthicknesses which may be different. It is nevertheless possible to use adifferent first process fluid for plasma treatment carried out in thetwo first electrodes 20, 20 a, thus obtaining coating layers 102, 104 ofa different chemical nature.

By arranging further pairs of electrodes (not shown in the figures)downstream of the second pair of electrodes 20 a, 22 a or by causing thecoated sheet 10 to pass again between the interstices defined by thefirst and second pair of electrodes, it is possible to obtain amultiple-layer coating having a plurality of layers 106 arranged on topof the layers 102 and 104, as shown in FIG. 4 c.

FIGS. 5 a and 5 b show an alternative embodiment of the plant accordingto the invention in which numbers identical to those used in thepreceding figures refer to identical or equivalent parts.

In this case, an undulated sheet 10 of polycarbonate is coatedsuperficially such that the first and second electrode 20, 22 of eachpair having facing surfaces with the same undulated profilecorresponding to that of the sheet 10. The operating principles of thislatter plant are in any case similar to those described above withreference to the plant for coating a flat sheet 10.

FIG. 5 a shows, similar to FIG. 2 c, the case where the first outer facesurface 12 and the inner alveolar surface 16 are coated, while FIG. 5 bshows, similar to FIG. 2 d, the case where, in addition to thesesurfaces, the second outer face surface 14 is also coated.

Obviously, without modifying the principle of the invention, theconstructional details and the embodiments may be widely varied withrespect to that described purely by way of example, without therebydeparting from the scope of the invention as defined in the accompanyingclaims. For example, the plant according to the invention does not haveto necessarily be combined with an extruder, but may coat sheets whichhave been produced in another location and/or some time beforehand.

1. Plant for the plasma surface treatment of an alveolar sheet (10) ofplastic material having a first and a second outer face surface (12, 14)and an inner alveolar surface (16), said plant comprising means able toallow the simultaneous and independent treatment of each of said outersurfaces (12, 14) and inner surface (16) with a respective plasma (96,98, 100) with which a process fluid is associated, said fluid beingdeposited on one of said surfaces (12, 14, 16).
 2. Plant according toclaim 1, in which said treatment means comprise at least one firstelectrode (20) arranged facing the first outer surface (12) of the sheet(10) and provided with means for supplying a first carrier gas, able tobe converted into plasma, and a first process fluid.
 3. Plant accordingto claim 2, in which said treatment means comprise a second electrode(22) arranged facing the second outer surface (14) of the sheet (10)opposite the first electrode (20) so as to define an interstice andprovided with means for supplying a second carrier gas able to beconverted into plasma and a second process fluid.
 4. Plant according toclaim 2, in which said first electrode (20) has a modular structure andis formed by a plurality of modular elements (72) arranged insuccession, each element (72) comprising a metal body (74) acting as ananode and having, in the portion directed towards said interstice, acavity (76) which is open outwards and inside which conducting materialacting as a cathode (78) is arranged, a layer (80) of dielectricmaterial coating the walls of said cavity (76) and isolating the anode(74) from the cathode (78).
 5. Plant according to claim 4, in which saidmetal body (74) is provided with passages (86) for conveying adiathermic fluid, so as to allow the temperature of the element (72) tobe controlled.
 6. Plant according to claim 4 or 5, in which the surface(82) of the metal body (74) directed towards said sheet (10) is coatedwith ceramic material having a high secondary emission coefficient. 7.Plant according to any one of the preceding claims, in which saidtreatment means comprise means for supplying, inside the alveoli of saidsheet (10), a third carrier gas able to be converted into plasma and athird process fluid.
 8. Plant according to claim 3, in which said firstand second electrodes (20, 22) have facing surfaces with the sameundulated profile.
 9. Plant according to any one of claims 3 to 8,comprising a plurality of pairs of first electrodes (20, 20 a) andsecond electrodes (22, 22 a) arranged facing each other, said pairs ofelectrodes being arranged in succession along the displacement path ofthe sheet (10) and allowing a series of successive plasma treatments tobe carried out on the outer surfaces (12, 14) and inner surface (16) ofthe sheet (10).
 10. Use of a plant according to any one of the precedingclaims for the plasma surface treatment, continuously and at atmosphericpressure, of an alveolar sheet (10) of plastic material, in particularpolycarbonate, having a first and a second outer face surface (12, 14)and an inner alveolar surface (16).